Implemented zero-arg version of `:echo`

Also added Vim ignores to .gitignore because I am that strange that I
was developing VsVim from within vanilla Vim. I did finish up in VS 2013
with R# and VsVim tho. :)
Made echo parse an expression after it
Evaluate the expression parsed after :echo
First step to :echo &expandtab (echo option)

Plumbed enough of the "echo option" stuff through to get a unit test
working without breaking any others. The type inference of the F#
compiler seems to be a bit of a doozy.

I'm not entirely comfortable yet with what I had to do here. It seems to
me that VariableValue has been used in a both of places in which
Expression should have been used. Still, I will definitely need
@JaredPar to review this.
Echo toggle/boolean options/settings

This is preliminary implementation. There are holes to be filled, and it
should probably be cleaned up some.
+ Only works for options which can be toggled; needs to be implemented
  for other option types
+ Doesn't handle window options, but once it does, there may be
  duplication between it and `RunSet`.
+ Does handle option abbreviations
+ Has some ugly nested matches
+ Definitely need to get Jared to review once I've matured it a bit
Removed some unnecessary match statements

Simplified some of the complexity I had added in previous work by
replacing some of the unnecessary match statements I had added with
simpler code.

Also, reverted .gitignore to master state since I learned you can have a
global .gitignore.
Evaluate integer-valued options as expressions

Should a test for this be put elsewhere, instead of into the Echo suite?
I put it there because that is the feature I am working on. However, the
code that is in use is more general-purpose.
Evaluate string-values options as expressions

Same testing question as in last commit
Evaluable variables as expressions (and echo)
Evaluate window settings as expressions (and echo)
Extracted some methods from my spaghetti code

Tried to increase readability/maintainability by breaking down a large
method into smaller ones
Evaluate registers as expressions (and echo)
Merge branch 'implEcho'
Removed case which will never be matched

according to compiler warning that I hadn't previously noticed
Rolled back change I did not mean to check in

I set this so that I could run the unit tests via R# but I did not mean
to check it in. Reverted.
Merge pull request #1442 from Kazark/master

Implement :echo command and enhance expression evaluation